The present invention relates to a paper production process. In the present application the term xe2x80x9cpaper production processxe2x80x9d is intended to encompass the entire paper production process, i.e. from the defibration of the wood until the paper product is ready to be supplied to the market. The present invention also relates to paper obtainable by said process, whereby xe2x80x9cpaperxe2x80x9d is to be understood to include also board, paperboard, fibreboard, and cardboard, as well as any other similar cellulosic fibre containing product. Furthermore, the invention relates to paper making additives such as drainage and retention agents that may be used in such a process.
The paper making process usually involves the use of various additives in order to control the paper production process as such and/or the properties of the produced paper. Drainage and retention agents are among the most common paper making additives.
A wide variety of drainage and retention agents are known in the art. These additives are included in the papermaking stock in order to facilitate drainage and/or to increase adsorption of fine particles and additives onto the cellulose fibres so that they are retained with the fibres. The drainage and retention agents employed include natural and synthetic organic polymers, particles of inorganic materials and many combinations thereof. Usually, oppositely charged materials are used. Certain microsize particles, namely colloidal silica particles, in combination with cationic starch, such as for example disclosed in EP-B-41,056 is an example of a commonly used drainage and retention agent. The particles act as flocculants, binding the polymer molecules to larger aggregates.
A common feature of the drainage and retention agents referred to above is that they contain certain microsize particles, below referred to as microparticles. It would be desirable to be able to provide a paper production process in which othermicroparticles than those presently known in the art are used as that would provide, at least ceteris paribus, for a bigger supply of microparticles. In a drainage/retention agent it would be desirable to use microparticles that could provide, at least potentially, for better flocculation. Microparticles that could provide for all of this would of course be especially desirable.
Thus, the problem to be solved by the present invention is to provide a paper production process in which such microparticles are used. This problem has been solved by the present invention as defined by the appended claims.
The present invention generally relates to a process for the production of paper comprising cellulosic fibers, which comprises treating at least some of the fibers with microparticles, wherein the microparticles comprise shell-formed carbon allotrope particles. The present invention also relates to paper obtainable by said process, whereby xe2x80x9cpaperxe2x80x9d is to be understood to include also board, paperboard, fibreboard, and cardboard, as well as any other similar cellulosic fiber containing product. Furthermore, the invention relates to paper making additives such as drainage and retention agents that may be used in such a process.
The present invention relates to a process for the production of paper comprising cellulosic fibers, wherein at least some of the fibers are treated at some part of the process with microparticles comprising shell-formed carbon allotrope particles. It has been found that the particle charge density of these microparticles may greatly influence the effect of the drainage/retention agents. It would seem that microparticles having a high particle charge density provide for a potentially better flocculation in a drainage/retention operation. The reason for this is as follows:
In a drainage/retention operation, a cationic polymer and anionic microparticles form complex agglomerates in the stock, which agglomerates are bound together by the anionic microparticles, and the cationic polymer becomes associated with filler material having a more or less anionic surface. The cationic polymer also becomes associated with the cellulosic fibers and fines, both of which are anionic. Upon bonding, the association between the agglomerates and the cellulosic fibers provides flocculation. It would seem that a higher particle charge density of the anionic microparticles would provide for more anionic groups on the particle surface, in turn providing more bond sites and, as a consequence, potentially bigger agglomerate.
In the present application the term xe2x80x9cmicroparticlexe2x80x9d indicates a particle having a particle size of up to about 10 xcexcm, preferably up to about 100 nm, and most preferably up to about 20 nm.
The microparticles used in the present invention comprise shell-formed carbon allotrope particles, which may mean that each microparticle consists of one or more shellformed carbon allotrope particles, but may just as well mean that themicroparticles are only partly made up of shell-formed carbon allotrope particles whereas the other part is made up of some other substance.
By xe2x80x9cshell-formed carbon allotropexe2x80x9d is meant any carbon allotrope in which the atoms are arranged so as to form a shell, preferably a closed shell having an essentially spherical form. An open shell form, such as for instance the form of a tube with one or more openings, is however not excluded.
In a preferred embodiment of the present invention the shell form is defined by the atomic lattice, i.e. each unit of this lattice constitutes an individual shell. An illustrative and preferred example of this embodiment is of course the fullerene allotrope, e.g. a [60] fullerene or a [70]fullerene. It is however not ruled out that the shell-formed particles may be socalled xe2x80x9chollow carbon microbeadsxe2x80x9d as disclosed by K. Esumi et al in Colloids and Surfaces, A: Physicochem. Eng. Aspects 108 (1996) 113-116, in which the shell form is defined by a plurality of atomic lattice units.
In one embodiment, the shell-formed carbon allotrope comprises one or more heteroatoms, such as for instance a Si, B, N, S, or P atom. In a particular example, the carbon allotrope is a heterofullerene such as described in xe2x80x9cThe Chemistry of the Fullerenesxe2x80x9d by A. Hirsch, (Georg Thime Verlag, Stuttgart, New York 1994, chapter 9.4.2, page 196).
The carbon allotrope particles may be furnished with addends and/or substituents; the particles may for instance be hydroxylated, sulphonated, or carboxylated. For instance, carbon allotrope particles may be polyhydroxylated fullerene derivatives, so-called fullerols, e.g. prepared according to the methods described by Jing Li et al in J. Chem. Soc., Chem. Commun., 1993, pp 1784-5 (xe2x80x9cC60 Fullerol Formation catalysed by Quartenary Ammonium Hydroxidesxe2x80x9d), or EP 540 311.
The invention can be used in a variety of flocculation operations, including for instance sludge dewatering, waste water treatment, wine clarification; this listing of flocculation operations is of course not exhaustive.
In one embodiment the particles are used for the purpose of improving the dewatering/retention performance of a paper making process, whereby the microparticles are preferably combined with a polymer. The particles and the polymer are added, either mixed or separated from each other, either simultaneously or consecutively, to the papermaking stock, whereby the shell-formed carbon allotrope particles are at least partially hydrophilic, and preferably soluble in aqueous solutions. In this embodiment the carbon allotrope is preferably an anionic fullerene derivative, e.g. a hydroxylated, sulphonated, or carboxylated fullerene derivative. When used for dewatering/retention performance improvement, the carbon allotrope particles are preferably associated with each other, e.g. by means of covalent bonds, electrostatic bonds, ionic bonds, or any similar kind of bonds. The bonds may for instance be constituted by means of one or more hydrocarbyl groups and/or one or more atoms chosen among N, O, P, S, B, and Si. Said atoms may form an integrated part of the particles or be comprised in an addend or substituent to the particles, but may also form a bridge between addends or substituents of two or more allotrope particles. The hydrocarbyl group may be an addend or substituent common to two or more allotrope particles, but may also form a bridge between addends or substituents of two or more allotrope particles, for instance between atoms chosen among N, O, P, S, B, and Si. The concept of fullerene polymers is discussed in xe2x80x9cThe Chemistry of the Fullerenesxe2x80x9d by A. Hirsch, (Georg Thime Verlag, Stuttgart, New York 1994, chapter 3.2.3, page 64-65), and one way to prepare such fullerene polymers is for instance disclosed in U.S. Pat. No. 5,367,051.
The allotrope microparticles may for instance be combined with a polymer having a branched or unbranched hydrocarbon chain, with or without substituents; it may for instance be chosen among starches, chitosans, seed gums such as guar gums, acrylamide-based polymers, poly(diallyidimethyl ammonium chloride), polyethylene imines, polyamines, polyamidoamines, melamine-formaldehyde resins, urea-formaldehyde resins, N-vinylamidebased polymers, or a combination thereof. In one preferred embodiment the polymer has a branched hydrocarbon chain.
Preferably, when used for dewatering/retention purposes, the allotrope microparticles are present in the papermaking stock in an amount of at least 0.005 kg/tonne of pulp, particularly preferred in an amount from about 0.03 to 5 kg/ton of pulp. The unit kg/ton is calculated as dry on dry fibres and optional fillers, and by a xe2x80x9ctonxe2x80x9d is meant a metric ton.
The present invention also relates to paper obtainable from this dewatering/retention performance improved paper making process.
Furthermore, the present invention relates to a drainage or retention agent comprising at least partially hydrophilic, anionic microparticles comprising shell-formed carbon allotrope particles, which is adapted to be used in said dewatering/retention performance improved paper making process. The partially hydrophilic, anionic microparticles are at least partially made up of carbon allotrope particles that are associated with each other, e.g. by means of covalent bonds, electrostatic bonds, ionic bonds, or any similar kind of bonds. The bonds may for instance be constituted by means of one or morehydrocarbyl groups and/or one or more atoms chosen among N, O, P, S, B, and Si. Said atoms may form an integrated part of the particles or be comprised in an addend or substituent to the particles, but may also form a bridge between addends or substituents of two or more allotrope particles. The hydrocarbyl group may be an addend or substituent common to two or more allotrope particles, but may also form a bridge between addends or substituents of two or more allotrope particles, for instance between atoms chosen among N, O, P, S, B, and Si.